What term names an electric bus powered by dual overhead wires?

An electric bus powered by dual overhead wires is a trolleybus. The two wires form a complete electrical circuit: one supplies current and the other provides the return path, collected by two trolley poles or other current collectors.

This distinguishes a trolleybus from a tram, whose steel rails usually provide the return circuit, and from a battery-electric bus, which stores energy onboard. The wires are generally suspended above ordinary roads, so a trolleybus needs no rails and can steer like a conventional bus, although its route is constrained by the overhead network.

The technology dates to Werner von Siemens’s 1882 Elektromote demonstration near Berlin. Modern trolleybuses may also carry batteries or auxiliary power units, allowing short off-wire movements. Even with that capability, a vehicle designed around overhead electric collection remains a trolleybus.